minor symfony#92 remove link to sensio extra bundle which removed psr7 support (Tobion)

This PR was merged into the 2.1-dev branch.

Discussion
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remove link to sensio extra bundle which removed psr7 support

The documentation that has been removed in extra bundle in sensiolabs/SensioFrameworkExtraBundle@8c9318d should probably be added to the bridge now.

Commits
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7078739 remove link to sensio extra bundle which removed psr7 support

Author: derrabus

README.md

@@ -7,7 +7,6 @@ Resources
 ---------
 
   * [Documentation](https://symfony.com/doc/current/components/psr7.html)
-  * [SensioFrameworkExtraBundle](https://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/index.html#psr-7-support)
 
 Running the tests
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